compile failed

[wbtlb]

Hi, could you please give some help for this problem
skeleton/pid_iter.bpf.c:35:10: error: incomplete definition of type 'struct bpf_link'
return BPF_CORE_READ((struct bpf_link *)ent, id);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/vagrant/linux-5.9.1/tools/lib/bpf/bpf_core_read.h:257:3: note: expanded from macro 'BPF_CORE_READ'
___type((src), a, ##VA_ARGS) __r;
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/vagrant/linux-5.9.1/tools/lib/bpf/bpf_core_read.h:181:29: note: expanded from macro '___type'
#define ___type(...) typeof(___arrow(VA_ARGS))
^~~~~~~~~~~~~~~~~~~~~
/vagrant/linux-5.9.1/tools/lib/bpf/bpf_core_read.h:179:23: note: expanded from macro '___arrow'
#define ___arrow(...) ___apply(___arrow, ___narg(VA_ARGS))(VA_ARGS)
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
note: (skipping 1 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all)
/vagrant/linux-5.9.1/tools/lib/bpf/bpf_core_read.h:130:25: note: expanded from macro '___concat'
#define ___concat(a, b) a ## b
^
:16:1: note: expanded from here
___arrow2
^
/vagrant/linux-5.9.1/tools/lib/bpf/bpf_core_read.h:170:26: note: expanded from macro '___arrow2'
#define ___arrow2(a, b) a->b
~^
skeleton/pid_iter.bpf.c:35:32: note: forward declaration of 'struct bpf_link'
return BPF_CORE_READ((struct bpf_link *)ent, id);
^
skeleton/pid_iter.bpf.c:35:10: error: incomplete definition of type 'struct bpf_link'
return BPF_CORE_READ((struct bpf_link *)ent, id);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/vagrant/linux-5.9.1/tools/lib/bpf/bpf_core_read.h:258:3: note: expanded from macro 'BPF_CORE_READ'
BPF_CORE_READ_INTO(&__r, (src), a, ##VA_ARGS);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/vagrant/linux-5.9.1/tools/lib/bpf/bpf_core_read.h:220:3: note: expanded from macro 'BPF_CORE_READ_INTO'
___core_read(bpf_core_read, dst, (src), a, ##VA_ARGS)
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/vagrant/linux-5.9.1/tools/lib/bpf/bpf_core_read.h:210:2: note: expanded from macro '___core_read'
___apply(___core_read, ___empty(VA_ARGS))(fn, dst,
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
note: (skipping 3 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all)
/vagrant/linux-5.9.1/tools/lib/bpf/bpf_core_read.h:204:2: note: expanded from macro '___core_read0'
___read(fn, dst, ___type(src), src, a);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/vagrant/linux-5.9.1/tools/lib/bpf/bpf_core_read.h:184:59: note: expanded from macro '___read'
read_fn((void )(dst), sizeof((dst)), &((src_type)(src))->accessor)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~
/vagrant/linux-5.9.1/tools/lib/bpf/bpf_core_read.h:119:56: note: expanded from macro 'bpf_core_read'
(const void *)__builtin_preserve_access_index(src))
^~~
skeleton/pid_iter.bpf.c:35:32: note: forward declaration of 'struct bpf_link'
return BPF_CORE_READ((struct bpf_link *)ent, id);
^
skeleton/pid_iter.bpf.c:35:10: error: returning 'void' from a function with incompatible result type '__u32' (aka 'unsigned int')
return BPF_CORE_READ((struct bpf_link *)ent, id);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/vagrant/linux-5.9.1/tools/lib/bpf/bpf_core_read.h:256:2: note: expanded from macro 'BPF_CORE_READ'
({
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
skeleton/pid_iter.bpf.c:42:17: warning: declaration of 'struct bpf_iter__task_file' will not be visible outside of this function [-Wvisibility]
int iter(struct bpf_iter__task_file *ctx)
^
skeleton/pid_iter.bpf.c:44:25: error: incomplete definition of type 'struct bpf_iter__task_file'
struct file *file = ctx->file;
~~~^
skeleton/pid_iter.bpf.c:42:17: note: forward declaration of 'struct bpf_iter__task_file'
int iter(struct bpf_iter__task_file *ctx)
^
skeleton/pid_iter.bpf.c:45:32: error: incomplete definition of type 'struct bpf_iter__task_file'
struct task_struct *task = ctx->task;
~~~^
skeleton/pid_iter.bpf.c:42:17: note: forward declaration of 'struct bpf_iter__task_file'
int iter(struct bpf_iter__task_file *ctx)
^
skeleton/pid_iter.bpf.c:76:19: error: incomplete definition of type 'struct bpf_iter__task_file'
bpf_seq_write(ctx->meta->seq, &e, sizeof(e));
~~~^
skeleton/pid_iter.bpf.c:42:17: note: forward declaration of 'struct bpf_iter__task_file'
int iter(struct bpf_iter__task_file *ctx)
^
1 warning and 6 errors generated.
make[1]: *** [Makefile:146: pid_iter.bpf.o] Error 1
make[1]: Leaving directory '/vagrant/linux-5.9.1/tools/bpf/bpftool'
make: *** [Makefile:46: bpftool] Error 2

[uablrek]

Bumped into this for linux-5.16.1. The problem arises if you have;

Auto-detecting system features:
...               clang-bpf-co-re: [ on  ]

Do;

CLANG=Nope make -j8

and it builds fine.